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sitional reactivity are observed upon bromination. As can be seen from Table 3, 7-bromo- (71), 4,7-dibromo- (72), 2,4,7-tribromo- (73), 2,4,6,7-tetrabromomelatonins (74), 68, 69, 3,4,7-tribromo- (75), and 4,7-dibromo-2-oxindoles (76) are produced depending on the quantity of Br2 [25].

The results shown in Tables 2 and 3 clearly demonstrate that the 1-methoxy group promotes selective bromination at the 7-position. This phenomenon can be explained by the following working hypothesis, either electrophilic (A) or nucleophilic mechanisms (B), as illustrated in Fig. 1 [25].

In the former mechanism, the bromonium ion initially approaches the indole ring and forms a n-complex (C). Then a coordination bond develops between the bromonium ion and the lone pair of 1-methoxy oxygen that is

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